The Project: Bacteria in the Order Rickettsiales cause significant morbidity and mortality in humans and animals. While the host range of the Rickettsiales varies, all require vectors for transmission. The genera Anaplasma and Ehriichia, including the organisms responsible for human anaplasmosis and human ehrlichiosis, require an ixodid tick vector for transmission from a mammalian reservoir to a susceptible host. This transmission requires the pathogen to enter the midgut of the tick, replicate, migrate to the salivary glands, and replicate again prior to transmission. The underlying mechanisms of this development within the vector represent a major gap in our knowledge of rickettsial pathogenesis. I propose to examine these pathways using a comparative genomic approach utilizing A. marginale as the experimental model. Sequencing of a non-transmissible strain and alignment with a previously sequenced tick transmissible strain will produce a list of polymorphisms. These will be examined in multiple tick-transmitted strains to eliminate differences not involved in tick transmissibility and produce a list of candidate genes. Candidates will be tested for involvement in tick transmission by molecular complementation of the nontransmissible strain. When successfully completed, this study will produce a list of genes necessary for tick transmission in A. marginale. Comparison of related rickettsial organisms will allow for discovery of common mechanisms of vector invasion, which can then be exploited for disease control strategies. The Candidate: The candidate is a veterinarian completing a residency in comparative anatomic pathology and a Ph.D. degree. The candidate has fulfilled most of the requirements of his pathology training along with all didactic course work and his candidacy exam, and is actively pursuing the research portion of his training. This research proposal constitutes his plan to investigate mecahnisms of vector transmission of rickettsial pathogens. Environment: The Department of Veterinary Microbiology and Pathology at Washington State University provides both modern research facilities for infectious disease research and a highly interactive training environment including intra- and interdisciplinary graduate education, residency programs, and extensive collaboration both within and ouside the university. The sponsors collaborate closely in research and have successfully mentored clinicians, graduate students, and post-doctoral fellows to research independence.